Pneumatic tire having a belt member

ABSTRACT

A pneumatic tire having a carcass of at least one rubberized sheet including cord elements of flexible material, a tread portion mounted on but spaced from the carcass, and a breaker member mounted between the carcass and tread portion. The breaker member consists of at least two groups of sheets including parallel cord elements with different modulus of elasticity for each sheet. The groups each include at least a pair of sheets with the cord elements of the first group deviating from the equatorial direction of the tire by a first angle and the second group at a second angle larger than the first angle.

United States Patent Mukai et al.

[ 51 Feb. 22, 1972 [54] PNEUMATIC TIRE HAVING A BELT MEMBER [72]Inventors: Tsuneo Mukai; Toshiro Tezuka, both of Tokyo, JapanBridgestone Tokyo, Japan [22] Filed: Sept. 29, 1966 [21] Appl.No.:582,961

[73] Assignee:

[30] Foreign Application Priority Data Mar. 11, 1966 Japan .Q ..4l/l460l[52] U.S.Cl 4.152/361, 152/354 [51] Int. Cl. ..B'60c 9/18 [58]FieldotSearch ..152l36l,354, 355,356

[56] References Cited UNITED STATES PATENTS 2,782,830 2/1957 Wallace152/361 Tire Company Limited,

3,115,921 12/1963 Leibee ..l52/36l 3,242,965 3/ l 966 Mirtain 152/361FOREIGN PATENTS OR APPLICATIONS 700,790 12/1964 Canada l 52/ 354 944,87612/1963 Great Britain ..l52/36l Primary ExaminerArthur L. La PointAssistant ExaminerRichard A. Bertsch Attorney-Stevens, Davis, Miller &Mosher ABSTRACT A pneumatic tire having a carcass of at least onerubberized sheet including cord elements of flexible material, a treadportion mounted on but spaced from the carcass, and a breaker membermounted between the carcass and tread portion. The breaker memberconsists of at least two groups of sheets including parallel cordelements with different modulus of elasticity for each sheet. The groupseach include at least a pair of sheets with the cord elements of thefirst group deviating from the equatorial direction of the tire by afirst angle and the second group at a second'angle larger than the firstangle.

10 Claims, 11 Drawing Figures PATENTEUFEB22 me I 3.643.723

SHEET 1. OF 6 Slip angle (degree) Self-aligning torque (kg m) A Slipangle (degree) v PATENTEBFEB22 are 3.643. 723

sum 2 or 6 i2 f Tension H 9 IO PATENTEDFEB 22 I972 3. 643 723 sum 5 or 6Slip angle (degree) Self-aligning torque (kg-m) Wang/e (degree)PNEUMATIC TIRE HAVING A BELT MEMBER This invention relates to animproved pneumatic tire having a belt member.

ln order to reduce wearing loss of the tread portion of a pneumatictire, a belt member having substantially the same width as that of thetread portion of the tire has been heretofore used by inserting itbetween the tread portion and the carcass of such a pneumatic tire. Sucha belt member, which is also referred to as a breaker member, comprisesa rubberized sheet including reinforcing elements or a plurality of suchrubberized sheets laminated each other.

Metal wires have been used as the reinforcing elements in such laminatedsheets of the breaker member of a pneumatic tire. In case of thepneumatic tire thus reinforced, the metal wires are arranged in parallelin each sheet and secured by rubberizing, and the wires in adjacentrubberized sheets run in three different directions, thus producingso-called triangulation," which are bonded together rigidly so that ahigh resistance may be provided against relative movement of eachrubberized sheet within the breaker member. The breaker member of theaforementioned construction acts to provide the tread portion of thetire with a high rigidity against deformation in both itscircumferential and transverse directions, and hence, the wearing lossof the tire tread can be reduced to a great extent.

On the other hand, the pneumatic tire comprising breaker member of suchhigh rigidity has disadvantages in that the maneuverability of vehiclesequipped with such tires is low, and that comfortableness to the driverof the vehicles is inferior due to the fact thatvibrations and noises ofsuch vehicles are high.

ln the aforementioned breaker member including metal wires arranged inthe above triangular relations, at least three sheets having metal wiresembedded therein in parallel have been laminated in such a fashion thatthe metal wires in different sheets intersect with the equatorialdirection of the tire at three different angles. If three such sheetsare used, the angles between the metal wires of the sheet and theequatorial direction of the tire (to be referred to as the cord angle"hereinafter) for the first two sheets have been selected in the range of17 to 28, whilst the corresponding cord angle of the third sheet hasbeen selected in the range of 45 to 90. The inventors noticed the factthat the disadvantageous operative properties of such tires to bedescribed in detail hereinafter, such as their cornering forcecharacteristics and self-aligning torque characteristics for differentslip angles, were caused by the excessive rigidity of the tread portionof the tire.

As means for obviating the above shortcomings of the tire ofaforementioned construction by reducing the rigidity of its treadportion, one can easily think of substitution of the metal wires withcord elements made of other flexible materials, such as natural resins,synthetic resins, and other inorganic flexible materials. However, ifthe cord elements made of such flexible materials are used in the samemanner as the metal wires of the tire of aforementioned construction,namely with the cord angles in the ranges of 17 to 28 for the first twosheets and 45 to 90 for the third sheet, then the rigidity of the treadportion of the tire thus produced will be lowered too far from that ofthe tire including metal wires, and desired operative characteristicswill not be obtained.

Furthermore, as a means to obviate the aforementioned difficulties ofthe tire including metal wires disposed in a socalled triangulationfashion, it has been already proposed to use cord elements disposed inthe breaker member ofa tire at zero inclination or a small angle to theequatorial direction of the tire. However, such tires including cordelements disposed at zero inclination or a small angle to the equatorialdirection of the tires proved to have serious drawbacks in that theirrigidity was too low, resulting in excessively low ability to generatethe cornering force, which led to very poor operative characteristics ofvehicles equipped with such tires.

The inventors have found, as a result of their years of various studies,that it is possible to provide a novel tire having the proper level ofrigidity while maintaining the high level of maneuverability withoutcausing any increase in the wearing loss of the tire.

According to a preferred embodiment of the invention, there is provideda pneumatic tire having a breaker member, comprising a pair of beadportions including metal wires, a carcass extending between said pair ofbead portions substantially in radial directions radiating from the axisof rotation of the tire, said carcass consisting of at least onerubberized sheet including cord elements made of flexible material, atread portion mounted on said carcass with a suitable spacing betweenthem, and a breaker member inserted between said tread portion and saidcarcass, said breaker member consisting of at least a first group ofsheets including cord elements of a certain modulus of elasticity and asecond group of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair of sheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial 5 direction by a second angle onopposite sides of the quator,

said second angle being larger than said first angle.

In each sheet of the cord member according to the present invention, itis permissible to use cord elements made of either metal wires or othersuitable flexible materials, such as natural resins, synthetic resins,and other inorganic flexible materials. If a breaker member is preparedby laminating at least four rubberized sheets comprising cord elementsmade of suitable flexible materials in the angular relations accordingto the present invention and by vulcanizing the sheets thus laminated,then there will be formed in the breaker member a structure consistingof a number of parallelograms defined by the cord elements disposed atcomparatively small cord angles, say in the range of 5 to 20, and thosecord elements disposed at comparatively large cord angles, say in therange of 13 to 50, act to reinforce said structure consisting ofaplurality of parallelograms in a very effective manner, and hence, thebreaker member acts to provide suitable rigidity to the tread portion ofthe tire ofthe invention.

Therefore, an object of the invention is to provide a tire having highstability in conjunction with excellent maneuverability by forming thetread portion of the tire so as to have the most suitable rigidity.

Another object of the invention is to provide a novel tire havingimproved resistivity against wearing loss in both equatorial and lateral(perpendicular to the equator) directions of the tire withoutsacrificing the ability to ensure the high level ofcomfortableness ofthe driver.

A further object of the invention is to provide a pneumatic tire havingexcellent resistivity against wearing of its tread portion even when itis subjected to a great number of repeated turning operations along acurved path.

For a better understanding of the invention, reference is made to theaccompanying drawings, in which;

FIG. 1 illustrates curves representing the magnitude of cornering forcesof a conventional radial tire and a pneumatic tire of ordinaryconstruction for different slip angles;

FIG. 2 shows curves representing relations between the slip angle andthe self-aligning torque of the tires of FIG. 1;

FIG. 3 is a graph illustrating relations between the modulus ofelasticity ofa breaker cord element and the tension applied thereto;

FIG. 4 is a fragmentary perspective view illustrating construction of apneumatic tire embodying the present invention, shown with a partthereof cut away;

FIG. 5 is a transverse sectional view of the tire, showing one halfthereof;

FIG. 6 is a diagrammatic illustration of the layout of different sheetsin a four-sheet breaker member embodying the invention;

FIGS. 7 and 8 are sectional views showing different embodiments of theinvention;

101024 (nan FIG, 9 is a greatly simplified diagrammatic illustration ofa preferred layout of the breaker cord elements according to theinvention; and

FIGS. 10a and 10b are curves illustrating the cornering forcecharacteristics and the self-aligning torque characteristicsrespectively of a conventional radial tire and a tire according to thepresent invention for different slip angles.

Generally speaking, when a vehicle equipped with pneumatic tires isgoing to turn round along a curved path, there are produced on the tirea cornering force and a self-aligning torque, of which magnitudes varyresponsive to the angle of deflection between the equatorial directionof the tire and the moving direction ofthe vehicle the (slip angle). Thecornering force acts to facilitate the movement of the vehicle along thecurved path, and the self-aligning torque acts to reduce the deflectionof the vehicle and the tire in order to facilitate movement of thevehicle and the tire along a linear path. The magnitude of theself-aligning torque is given as a product of the cornering force andthe distance between the center of that portion of the tire which is indirect contact with the road surface and the point where the corneringforce is applied to.

In the case ofa pneumatic tire having a breaker member including metalwires in a triangular fashion, there are peculiar relations between itscornering force and the slip angle and between its self-aligning torqueand the slip angle. Referring to FIG. I, in which the abscissarepresents the slip angle and the ordinate represents the corneringforce, the curve A designates the cornering force characteristics of apneumatic tire having a breaker member consisting of metal wiresdisposed in a triangular fashion. The curve l3 designates thecorresponding characteristics of a pneumatic tire of ordinaryconstruction, which has been commonly used heretofore.

In order to turn round a vehicle along a curved path, it is necessary toapply a centripetal force to the vehicle, so that the centrifugal forceacting on the vehicle, which is determined responsive to its weight,speed, radius of curvature of the path, etc., may be properlycompensated for. The substantial portion of such a centripetal force isproduced by the cornering force of the tire mounted on the vehicle. Incase of the curve A of FIG. 1, the maximum value of the cornering forceis produced when the slip angle is about 6, and as the slip angleincreases in excess of 6, the cornering force is reduced. On the otherhand, in case of the curve B the maximum value of the cornering force isgiven when the slip angle is about 14, and the maximum value of thecornering force is retained for larger slip angles in excess of 14.

The cornering force characteristics represented by the curve A is verydangerous for the driver ofa vehicle equipped with tires having saidcornering force characteristics. As long as the slip angle is less thanabout 6, or less than that slip angle which gives the maximum corneringforce according to the curve A,, the rate of generating cornering forceof the tire as represented by the curve A is larger than that of otherconventional tires such as the one represented by the curve B The highrate of generating cornering force responsive to the variation oftheslip angle generally gives the driver the feeling of high road holding,that is to say the driver feels that there will be no possibility ofskidding when he increases the slip angle by further turning thesteering wheel. In the case ofa tire having the characteristics shown bythe curve A the aforementioned feeling of high road holding is validonly for the small slip angle, and as soon as the slip angle exceeds acertain limit value, which is about 6 in the case of the curve A,, thenthe magnitude of the cornering force is gradually decreased from itsmaximum value, and consequently, the centrifugal force acting on thevehicle is not compensated in full any more, and the vehicle skids awayfrom its desired travelling path.

On the other hand, in case ofa conventional tire of ordinaryconstruction having the cornering force characteristics as shown by thecurve B in FIG. 1, the cornering force is increased slowly in accordancewith the increase of the slip angle, and hence, the driver of thevehicle can foresee the danger of skidding well before its occurrence sothat he may drive the vehicle safely.

Referring to FIG. 2, in which the abscissa represents the slip angle andthe ordinate shows the self-aligning torque, the curve A represents theself-aligning torque characteristics of a pneumatic tire having abreaker member consisting of metal wires disposed in a triangularfashion, and the curve B shows the similar characteristics of aconventional tire having ordinary construction. It is apparent from FIG.2 that the tire having the characteristics shown by the curve A producesa larger self-aligning torque than that of the tire of ordinaryconstruction as long as the slip angle is small. The reason for such adifference in the self-aligning torque characteristics of the two tiresis in the fact that the former tire has a tread portion having a higherrigidity than that of the latter tire.

According to the curve A of FIG. 2, as the slip angle is increased inthe region of less than three degrees, the self-aligning torque isincreased, while, if the slip angle exceeds 3, then the self-aligningtorque diminishes rapidly responsive to such increase of the slip angleuntil it reaches zero at the slip angle of about 9.

On the other hand, in case ofa tire of ordinary construction representedby the curve B the maximum value of the selfaligning torque is producedwhen the slip angle is about 6, which is larger than the correspondingslip angle of the curve A and the rate of decrease of the self-aligningtorque in the curve B is smaller than that of the curve A Theself-aligning torque characteristics of the curve A are also verydangerous for the driver of a vehicle equipped with tires having suchcharacteristics. In case ofa vehicle equipped with ordinary tires, asthe steering wheel is rotated to turn round the vehicle, the slip angleand accordingly self-aligning torque of the tires are increased, andhence, the driver feels reasonable resistance on the steering wheelresponsive to the increase of the self-aligning torque of the tires.However, if tires having self-aligning torque characteristicsrepresented by the curve A are used, then as the slip angle exceedsabout 3, the resistance felt by the driver on the steering wheel againstits further rotation is suddenly reduced, and hence, the normallyexpected feeling of the driver for the increased resistance on thesteering wheel responsive to the increase in its angular displacementfails. Thus, the driver may be bewildered and feel unrest upon failureof the occurrence of the expected resistivity on the steering wheel.

Furthermore, if the slip angle of the tire having the self-aligningtorque characteristics as shown by the curve A is increased in excess ofits critical angle, which is about 9, in order to turn along a verysharp path, then the driver has to apply a steering force to the tire ina direction opposite to what is ordinarily expected. Thus, the drivermay loose control of the vehicle. Such conditions are apparently verydangerous.

In addition, when one drives a vehicle equipped with the tire having thecharacteristics shown by the curve A at a slow or intermediate speed,the magnitude of the self-aligning torque is large for small slipangles, which requires a large force to be applied on the steeringwheel, and hence, the fatigue of the driver is increased accordingly.

The pneumatic tire having a breaker member consisting of metal wiresdisposed in a triangular fashion has another disadvantage in that therigidity of the tread portion of the tire is so high that the levels ofvibration and noise of a vehicle equipped with such tires are higherthan those caused by ordinary tires, and accordingly, the driver of thevehicle has to experience unendurable discomfort.

In order to obviate the above difficulties by reducing the rigidity ofthe tread portion of the tire while retaining the wearing loss of thetire at a low level, it has been proposed to arrange the cord elementsof the breaker member at zero inclination or a small angle to theequatorial direction of the tire. The wearing loss of the tread portionof the tire is generally caused by its local contraction in theequatorial direction (wiping action) responsive to its contact with theroad surface. With a breaker member of the above construction includingcord elements arranged at zero inclination or a small angle to theequatorial direction of the tire, the wearing loss of the tread portionmay be reduced not by increasing its 101024 man rigidity but bypreventing the occurrence of its creeping by stretching the breakermember with the internal air pressure of the tire. Thus, it is madepossible to allow a reduction in the rigidity of the tread portion.However, such reduction of its rigidity also causes a reduction of thecornering force of the tire, which is one of the most importantoperative properties of the tire, and hence, the overall operativecharacteristics of such a tire comprising zero inclination cord elementsbecomes inferior to those of the tire having the aforementioned breakermember including metal wires disposed in a triangular fashion.

The curve C, of FIG. 1 shows cornering force characteristics of a tirehaving a breaker member consisting of cord elements arranged at zeroinclination or a small angle to its equatorial direction. It is apparentfrom FIG. 1 that both the magnitude and the rate of generating thecornering force of the curve C, are considerably less than those of thecurve A, or the cornering force of the tire having a tread portion ofhigh rigidity in the range of small slip angles, say less than about andat the same time it is noticed that the maximum value of the corneringforce of the former tire is lower than that of the latter tire. It hasbeen known that such a low rate of generating cornering force results inpoor stability in the travelling directions of the vehicle at high speedand necessitates an increased angular displacement of the steering wheelwhen a vehicle is going to be turned round or proceeds along a curvedpath at a high speed, and accordingly, such tire is dangerous for adriver. The reduction in the maximum value of the cornering force makesit difficult to drive a vehicle along a curved path at a high speed, andif one dares to make a turn at a high speed with tires of low corneringforce characteristics, then the vehicle skids and he may lose control ofthe vehicle.

Furthermore, the above reduction in the rigidity of the tread portion ofthe tire tends to lower the resistance against wearing in its transversedirection.

As described in the foregoing, the reasons for wearing ofthe treadportion ofa tire have been heretofore believed to be due to mainly localcontractions of that tire tread portion which is in contact with theroad surface in both equatorial and transverse directions of the tire.The inventors, however, have found through experiments that when avehicle is turned round, tires of the vehicle are twisted at thoseportions where they are in direct contact with the road surfaceresponsive to the slip angle necessary for turning round, and that suchtwisting of the tires affects their wearing in a degree equivalent to orin excess of that of the above local contractions. In other words, if atire producing a high cornering force for a given slip angle is used,then the degree of twisting its tread portion is small for the givenslip angle, and hence the wearing loss of the tread portion ofthe tireis also small.

In the aforementioned two kinds of known pneumatic tires having cordelements arranged in a triangular fashion and at zero angle to theequatorial direction thereof respectively, the former tire has seriousdrawbacks in that its operative characteristics are dangerous due to theexcessively high rigidity of its tread portion, and that it does notprovide suitable comfortableness to the driver because of theexcessively high level ofits vibration and noise caused by the abovehigh rigidity. In fact, due to the aforementioned drawbacks, someautomobile manufacturers do not use the tire having metal wires embeddedtherein in so-called triangulation relation. On the other hand, thelatter tire has disadvantages in that its operative characteristics arealso unsatisfactory due to the excessively low rigidity of its treadportion, and that its wearing loss is too large caused by the above lowrigidity.

Other important factors affecting the operative characteristics of thepneumatic tire will now be described to further clarify the features ofthe invention.

When a pneumatic tire mounted on a vehicle is filled with air to asuitable pressure level and subjected to driving on a road, then thereare applied stresses both in the equatorial and transverse directions ofthe tire. Almost all of the stress in the equatorial direction of thetire is borne by the breaker member of the tire, and those cord elementsof the breaker member which are disposed at small cord angles bear mostof the stress while those cord elements which are disposed at large cordangles bear only very little of the stress.

FIG. 3 shows the modulus of elasticity of such cord elements toconstitute breaker members, in which the abscissa represents the stressapplied on the cord elements and the ordinate modulus of elasticity ofthe cord elements when they are elongated to a certain length (to bereferred to simply as the modulus of elasticity hereinafter). The curve:1 represents the modulus of elasticity of those cord elements which aredisposed at a comparatively small cord angle both in the conventionalbreaker member and the breaker member of the invention, the curve a themodulus of elasticity of cord elements disposed at a comparatively largecord angle in the conventional breaker member, the curve a the modulusof elasticity of the cord elements of curves a and a as measured priorto their vulcanization, and the curve b modulus of elasticity of cordelements disposed at a comparatively large cord angle in the breakermember according to the invention.

It has been a common practice in pneumatic tires of the kind to usereinforcing cord elements having substantially the same properties bothfor those to be arranged at comparatively large cord angles and forthose to be arranged at comparatively small cord angles. Suchreinforcing cord elements are assembled in rubberized sheets forming thebreaker member of the tire prior to its vulcanization, and hence, as thecircumference of the breaker member is elongated during the vulcanizingprocess of the tire, the reinforcing cord elements are also elongated.When the vulcanization is over, the cord elements are secured atelongated positions determined by various vulcanizing conditions, suchas the tensile force and heat applied to the cord elements during thevulcanizing process, etc.

Such elongation of each cord element causes an increase in its modulusofelasticity, and besides, in view of the fact that the degree ofelongation of the cord elements is varied as the cord angle of disposingthe cord elements in the breaker member is changed, it will beunderstood that upon completion of the vulcanizing process of the tire,the level of the modulus of elasticity of the cord elements disposed atsmall cord angles will be raised from that of the curve a" to that ofthe curve a and retained there, while the corresponding level of themodulus of elasticity of the cord elements disposed at large cord angleswill be also raised from that of the curve a" to that ofthe curve a andretained there.

As described in the foregoing referring to the findings of theinventors, when the tire is filled with air to a certain pressure level,those cord elements arranged at small cord angles act to bear a tensileforce T, representing a larger portion of the entire tension applied tothe belt by said air pressure and each cord element arranged at thesmall angle shares a part :1 of said tension T, to produce a modulus ofelasticity Mal, whilst those cord elements arranged at large cord anglesact to bear a tensile force T representing a smaller portion of theentire tension applied to the belt by said air pressure and each cordelement arranged at the large angle shares a part [2 of said tension Tto produce a modulus of elasticity Ma2, which is smaller than Mal.

Accordingly, in conventional pneumatic tire of this kind, thosereinforcing cord elements embedded in the breaker member at small cordangles have modulus of elasticity characteristics which are differentfrom those of cord elements disposed at large cord angles, as shown bycurves a and a of FIG. 3. Such difference in the modulus of elasticitytends to reduce the composite reinforcing effects of such cord elementshaving different cord angles. In addition, when the tire is filled withair to a certain pressure level, there is produced a difference oftensile stress, say (t1t2) in FIG. 3, between the cord elements arrangedat different angles, and hence, the difference in the modulus ofelasticity is further increased, say as large as (MalMa2). Thus, thecomposite reinforcing effects are further reduced.

On the other hand, according to a preferred form of the invention, thosecord elements having modulus of elasticity characteristics representedby the curve a of FIG. 3 when vulcanized are disposed in the breakermember at small cord angles with respect to the equatorial direction ofthe member,

while those cord elements having high modulus of elasticitycharacteristics represented by the curve b when vulcanized are disposedin the breaker member at large cord angles with respect to theequatorial direction thereof. Accordingly, the difference in modulus ofelasticity characteristics between the cord elements disposed atdifferent cord angles, such as those represented by (2-11), can beobviated even after vulcanization. In the pneumatic tire of theinvention, when the tire is pressurized by filling air therein, themodulus of elasticity Mb according to the curve b for the tensile stresst2 is selected to be the same as or close to that modulus of elasticityMal which is according to the curve a for the tensile stress 11 or to belarger than Mal. Thus, effective reinforcing action of the cord elementsis ensured.

With such effective reinforcing action of the cord elements, it is madepossible to provide desired rigidity to the tread portion of the tire bymeans of the breaker member of the invention. In other words, accordingto the principles of the invention, it is made possible to provide apneumatic tire having a tread portion ofideal rigidity by obviating boththe excessively high rigidity of the tread portion including a breakermember reinforced by rigid metal wires and the excessively low rigidityof the tread portion including a breaker member reinforced by cordelements disposed at zero inclination, which are made of flexiblematerial.

The breaker member according to the invention also results in costreduction because of the fact that cord elements having thecharacteristics shown by the curve I) of FIG. 3 can be prepared byutilizing only conventional materials, if so desired. For instance, thecord elements represented by the curve b of FIG. 3 can be made of thesame material as that of the curve a by processing it under properlyselected treating conditions, such as the way of twisting, the tensionto be applied to the cord elements during the process, etc, so that themodulus of elasticity of the former may become higher than that of thelatter. In view of the aforementioned fact that the use of reinforcingcord elements having a high modulus of elasticity as the cord elementsdisposed at large cord angles enables more effective reinforcement thanthat produced by using conventional reinforcing cord elements, it is nowmade possible to obtain a pneumatic tire having tread portion providedwith a higher rigidity than that of conventional tires even if thenumber of cord elements to be embedded therein is reduced. In otherwords, the pneumatic tire of the invention can be produced at a low costbecause various cord elements to be used in the tire at different cordangles can be made of the same material, and furthermore, the number ofsuch cord elements to be embedded in the breaker member of the tire canbe reduced to a level less than the corresponding number in conventionaltires.

It should be noted here that according to the principles of theinvention, the materials to be used for various cord elements of thepneumatic tire are not limited to be the same, but it is apparentlypermissible to use different materials for different reinforcing cordelements of the tire in order to fulfill the objects ofthe inventionmost effectively.

By utilizing the optimum rigidity of the tread portion of the pneumatictire of the invention, the cornering force characteristics andself-aligning torque characteristics of the tire can be improved to agreat extent, and at the same time, the wearing loss of the tire can beconsiderably reduced without causing any ill effects on the vibrationand comfortableness of a vehicle equipped with such tires.

The pneumatic tire of the invention will now be described in furtherdetail referring to different embodiments illustrated in the drawings.

Referring to FIGS. 4 and 5, the tire, which is generally represented bythe reference numeral 1, comprises a tread portion 2, a pair of sidewallportions 3, and a pair of bead portions 4. The tire is shown as mountedon the rim member 5. The pair of sidewall portions 3 are reinforced bymeans of a carcass 6 consisting of at least one rubberized sheet and byend portions 7 of the carcass folded around the bead rings 40 of thebead portion 4. The cord elements of the carcass 6 in this particularembodiment of the invention are disposed substantially along the radialdirections radiating from the axis of rotation of the tire. In otherwords, cord elements of the carcass are laid substantially in parallelwith each other at the tread portion of the tire so as to intersect withthe equatorial direction of the tire at right angles.

In order to provide proper reinforcement to the tread portion 2, thereis inserted a breaker member 8 between the tread portion 2 and thecarcass 6. In this particular embodiment, the breaker member 8 comprisesfour rubberized sheets 9, l0, l1 and 12. Each sheet 9, 10, 11, or 12 ismade ofa rubberized tire fabric comprising cord elements consisting ofhighly flexible materials, such as natural resins, synthetic resins, andother inorganic flexible materials. As shown in FIG. 6, the dispositionof the sheets 9 and 12 is such that the parallel cord elements of thesheet 9 are deviated from the equatorial direction of the tire by anangle of 13 degrees in one direction, while the elements of the sheet 12by the same angle of 13 but in the opposite direction. The sheets 10 and11 are sandwiched between the sheets 9 and 12 in such a manner that thedirection of the parallel cord elements of the sheet 10 is deviated fromthe equatorial direction of the tire by an angle of 33 in one direction,while that of the sheet 11 by the same angle of 33 in the oppositedirection. Those cord elements which are deviated from the equator ofthe tire by 13 have a modulus of elasticity of i5 gram/denier at anelongation of 2 percent, while those cord elements deviated by 33 have amodulus of elasticity of 2 gram/denier at an elongation of 2 percent.

FIG. 7 shows another embodiment of the invention, in which four sheets13, 14, 15, and 16 are used in the breaker member, however, the cordelements of the second and the fourth sheets 14 and 16 as counted fromthe farthest from the axis of the tire are deviated from the equatorialdirection of the tire by l3 on opposite sides thereof respectively,while those of the first and the third sheets 13 and 15 are deviatedfrom the equator by 33 on the opposite sides thereof respectively.

FIG. 8 shows still another embodiment of the invention, in which sixsheets 17, 18, 19,20, 21, and 22 are used to form the breaker member 8.In this embodiment, the sheets 17 and 22 are so disposed that cordelements thereof are deviated from the equatorial direction of the tireby an angle between 13 to 50. The cord elements of the sheets 18, 19,20, and 21 are deviated from the equator by angles between 5 to 20.

It is permissible to select different angles .of deviation of cordelements in each sheet of the breaker member within the aforementionedranges so as to attain different combinations of cord angles. Accordingto the invention, it is made possible to obtain a tread portion havingan excellent rigidity by disposing cord elements having different moduliof elasticity at different cord angles, as described in the foregoing.Furthermore, the rigidity of the tread portion of the tire can beselected as desired within a certain range by using proper combinationof the cord angles for different sheets in the breaker member thereof.

FIG. 9 is a simplified diagram illustrating the layout of cord elementsin the breaker member of a tire embodying the invention. Those cordelements deviated from the equatorial direction Q-Q of the tire by asmall angle a in opposite directions form a number of narrow and longparallelograms, such as those similar to a parallelogram ABCD of thefigure. In the figure, those cord elements deviated from the equator ofthe tire by a large angle ,8 in the opposite directions are indicated bylines EB, FD, GD, and HB, which are located inside of said parallelogramABCD. A diagonal line BD of the parallelogram of the figure represents acord element of the carcass lOlO24 6. It has been found throughexperiments that particularly good results are obtained when one selectsone cord angle a in i the range of to 20 while selecting the other cordangle ,8 which is larger than said angle a within the range of 13 to 50,so that those cord elements deviated by the angle ofB may intersect withthe sides of the parallelogram ABCD at intermediate points thereof. Bestresult has been obtained when those cord elements deviated by the largeangle intersect with the sides of the parallelogram at about the middlepoints E, F, G, and H thereof. Such cord elements are bonded together byrubber in the process of rubberizing and vulcanizing the sheets, andhence, each intersecting point of the cord elements acts as a node ofthe cord element mechanism of the breaker member. It is apparent fromFIG. 9 that each parallelogram formed by cord elements deviated by asmall angle a, such as the parallelogram ABCD, is reinforced by theother cord elements deviated by a large angle B from the equator of thetire. Accordingly, the breaker member consisting of such cord elementshas the optimum resistivity against strains caused by external forces,such as a force in the transverse direction PP of the tire, a forcealong the equatorial direction QQ of the tire, a force in a directionperpendicular to the plane defined by the parallelogram, and a compositeforce of last mentioned forces in various directions.

Furthermore, the breaker member of such construction acts to provide theoptimum rigidity to the tread portion of the tire even whennonmetalliccord elements are used therein. Such action of improving therigidity of the tire tread is further increased if those cord elementsdeviated from the equator by a large angle, such as EB, FD, GD, and H8in FIG. 9, are provided with a higher modulus of elasticity that that ofthose cord elements deviated by a small angle from the equator, such asAB, BC, CD, and DA ofFlG. 9.

FIG. 10a are curves representing the relations between the slip angleand the cornering force of different tires, in which the curve Drepresents said relations of a tire provided with a breaker memberaccording to the invention, the curve A said relations of a tire havinga breaker member consisting of cord elements in a triangular fashion asdescribed hereinbefore, and the curve C;, said relations of a tirehaving a breaker member consisting of cord elements disposed at zeroinclination or small angle to the equator thereof. If one compares thecornering force characteristics D of the tire according to the inventionand the similar characteristics A of the tire including metal wiresdisposed in a triangular fashion, it is apparent that while thecornering force of the tire of the invention is slightly smaller thanthat of the tire having said metal wires in the range of small slipangles, however, the dangerous decrease of cornering force form acertain maximum value responsive to the increase of the slip angle inexcess of a certain critical angle, which is about 6 in case of thecurve A is completely eliminated in the tire of the invention.

It should be noted here that not only the aforementioned decrease of thecornering force, but quick saturation of the cornering force in theaforementioned tire having metal wires is also dangerous, because thedriver cannot foresee such quick saturation beforehand, the corneringforce of the tire of the invention is increased at a rate slower thanthat of the aforementioned tire having metal wires disposed in so-calledtriangulation.

Furthermore, the cornering force characteristics of the tire accordingto the invention are such that its increasing trend is maintained evenwhen the slip angle increases beyond 14".

On the other hand, in comparison of the cornering force characteristicsD of the tire according to the invention against the cornering forcecharacteristics C of a tire having a reduced rigidity at the treadportion thereof, the characteristics C is free from the dangerousdecrease of the cornering force as indicated in the curve A however, thegeneral level of the cornering force of the curve C is considerablylower than that of the curve D and hence, the maximum cornering force ofthe former is also smaller than that of the latter,

In short, with the cornering force characteristics of the tire of theinvention as represented by the curve D it is made possible to obviateshortcomings of conventional tire characteristics as represented by thecurves A and C and thus, high stability together with excellent steeringcharacteristics-of the tire can be obtained.

FIG. 1012 shows the relations between the slip angle and theself-aligning torque of different tires, in which the curve A,represents said relations of a tire including metal -wires disposed in atriangular fashion, and the curve D said relations of the tire of theinvention. It is apparent from the figure that maximum value of theself-aligning torque occurs in the case of the tire of the invention ata larger slip angle than that in the case of the conventional tirehaving said metal wires. After the maximum values of the self-aligningtorques are reached, the rate of decrease of the self-aligning torque ofthe tire of the invention is smaller than that of the curve A,, andhence, that slip angle which corresponds to zero self-aligning torque incase of the tire of the invention is larger than that in case of theconventional tire represented by the curve A In addition, in view of thefact that the self-aligning torque of the tire of the invention forsmall slip angles is smaller than that of said conventional tire, it ispossible to control the steering wheel with a smaller force with thetires of the invention than that with said conventional tires.Therefore, the excellent selfaligning torque characteristics of the tireof the invention make it possible to provide excellent operativeproperties to a vehicle equipped with said tires.

In order to clarify the advantages of the tire of the invention, itswearing loss was measured, and it was ascertained through experimentsthat the wearing loss of the tire of the invention was less by about 30percent than that ofa tire having a breaker member consisting of cordelements disposed substantially at zero inclination or small angle tothe equator thereof. The excessive vibration and noise accompanying thetire including metallic cord elements disposed in a triangular fashionare eliminated completely in the tire of the invention. Thereby, thetire of the invention enables the improvement of the comfortableness ofthe driver of the vehicle equipped with pneumatic tires while retainingthe same level of wearing loss as that of the tire including metal wiresembedded therein in a triangular fashion.

The invention has been described in the foregoing by referring toparticular embodiments thereof, however, it should be understood that anumber of different modifications are possible within the scope oftheinvention.

What we claim is:

l. A pneumatic tire having a breaker member, comprising a pair of beadportions including metal wires, a carcass extending between said pair ofbead portions substantially in radial directions radiating from the axisof rotation of the tire, said carcass consisting of at least onerubberized sheet including cord elements made of flexible material, atread portion mounted on said carcass with a suitable spacing betweenthem, and a breaker member inserted between said tread portion and saidcarcass, said breaker member consisting of at least a first group ofsheets including cord elements of a certain modules of elasticity and asecond group of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair ofsheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial direction by a second angle onopposite sides of the equator, said second angle being larger than saidfirst angle, said first angle being in the range of 5 to 17, said secondangle being in the range of 13 to 50, and said certain modules ofelasticity of the first group of sheets being smaller than that of saiddifferent modules of elasticity of said second group of sheets said cordelements of said second group of sheets intersecting with at least oneparallelogram formed by the cord elements of said first group of sheetsat an apex ofa large interior angle of said one parallelogram.

2. A pneumatic tire according to claim 1, wherein said breaker membercomprises four sheets, and the first and the fourth sheets thereofcounted from the axis of rotation of the tire constitute said firstgroup while the remaining sheets thereof constitute said second group.

3. A pneumatic tire according to claim 1, wherein said breaker membercomprises four sheets, and the second and the fourth sheets thereofcounted from the axis of rotation of the tire constitute said secondgroup, while the remaining sheets thereofconstitute said first group.

4. A pneumatic tire according to claim 1, wherein said breaker membercomprises four sheets, and the second and third sheets thereof countedfrom the axis of rotation of the tire constitute said first group, whilethe remaining sheets thereof constitute second group.

5. A pneumatic tire according to claim 1, wherein said breaker membercomprises six sheets, and the first and last sheets thereof counted fromthe axis of rotation of the tire constitute said first group, while theremaining sheets thereof constitute said second group.

6. A pneumatic tire according to claim 1, wherein said breaker membercomprises six sheets, and the first and last sheets thereof counted fromthe axis of rotation of the tire constitute said second group, while theremaining sheets thereof constitute said first group.

7. A pneumatic tire according to claim 1, wherein said breaker membercomprises six sheets, and the third and fourth sheets thereof countedfrom the axis of rotation of the tire constitute said first group, whilethe remaining sheets thereof constitute said second group.

8. A pneumatic tire according to claim 1, wherein said cord elements ofsaid breaker member are made of flexible materials selected from thematerials consisting of natural resins, synthetic resins, glass fibermaterials.

9. A pneumatic tire having a breaker member, comprising a pair of beadportions including metal wires, a carcass extending between said pair ofbead portions substantially in radial directions radiating from the axisof rotation of the tire, said carcass consisting of at least onerubberized sheet including cord elements made of flexible material, atread portion mounted on said carcass with a suitable spacing betweenthem, and a breaker member inserted between said tread portion and saidcarcass, said breaker member consisting of at least a first group ofsheets including cord elements of a certain modulus of elasticity and asecond group of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair of sheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial direction by a second angle onopposite sides of the equator. said second angle being larger than saidfirst angle. said first angle being in the range of 5 to l7, said secondangle being in the range of 13 to 50, and said certain modulus ofelasticity of the first group of sheets being smaller than that of saiddifferent modulus of elasticity of said second group of sheets, saidcord elements of said second group of sheets intersect with at least oneparallelogram formed by the cord elements of said first group of sheetsboth at an apex of a large interior angle of said one parallelogram andat about the middle point of that side of said one parallelogram whichis opposite to said apex thereof. 1

10. A pneumatic tire having a breaker member, comprising a pair of beadportions including metal wires a carcass extending between said pair ofbead portions substantially in radial directions radiating from the axisof rotation of the tire, said carcass consisting of at least onerubberized sheet including cord elements made of flexible material, atread portion mounted on said carcass with a suitable spacing betweenthem, and a breaker member inserted between said tread portion and saidcarcass, said breaker member consisting of at least a first group ofsheets including cord elements of a certain modulus of elasticity and asecond group of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair of sheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial direction by a second angle onopposite sides of the equator, said second angle being larger than saidfirst angle, said first group comprising a pair of sheets including cordelements having a modulus of elasticity of 1.5 gram/denier at anelongation of 2 percent said sheets of the first group being deviatedfrom the equatorial direction of the tire by 13 on opposite sides ofsaid equatorial direction, and said second group comprising a pair ofsheets including cord elements having a modulus of elasticity of 2gram/denier at an elongation of 2 percent, said sheets of the secondgroup deviating from the equatorial direction of the tire by 33 onopposite sides of said equatorial direction.

lOl024 (1744

1. A pneumatic tire having a breaker member, comprising a pair of beadportions including metal wires, a carcass extending between said pair ofbead portions substantially in radial directions radiating from the axisof rotation of the tire, said carcass consisting of at least onerubberized sheet including cord elements made of flexible material, atread portion mounted on said carcass with a suitable spacing betweenthem, and a breaker member inserted between said tread portion and saidcarcass, said breaker member consisting of at least a first group ofsheets including cord elements of a certain modules of elasticity and asecond group of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair of sheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial direction by a second angle onopposite sides of the equator, said second angle being larger than saidfirst angle, said first angle being in the range of 5* to 17*, saidsecond angle being in the range of 13* to 50*, and said certain modulesof elasticity of the first group of sheets being smaller than that ofsaid different modules of elasticity of said second group of sheets saidcord elements of said second group of sheets intersecting with at leastone parallelogram formed by the cord elements of said first group ofsheets at an apex of a large interior angle of said one parallelogram.2. A pneumatic tire according to claim 1, wherein said breaker membercomprises four sheets, and the first and the fourth sheets thereofcounted from the axis of rotation of the tire constitute said firstgroup while the remaining sheets thereof constitute said second group.3. A pneumatic tire according to claim 1, wherein said breaker membercomprises four sheets, and the second and the fourth sheets thereofcounted from the axis of rotation of the tire constitute said secondgroup, while the remaining sheets thereof constitute said first group.4. A pneumatic tire according to claim 1, wherein said breaker membercomprises four sheets, and the second and third sheets thereof countedfrom the axis of rotation of the tire constitute said first group, whilethe remaining sheets thereof constitute second group.
 5. A pneumatictire according to claim 1, wherein said breaker member comprises sixsheets, and the first and last sheets thereof counted from the axis ofrotation of the tire constitute said first group, while the remainingsheets thereof constitute said second group.
 6. A pneumatic tireaccording to claim 1, wherein said breaker member comprises six sheets,and the first and last sheets thereof counted from the axis of rotationof the tire constitute said second group, while the remaining sheetsthereof constitute said first group.
 7. A pneumatic tire according toclaim 1, wherein said breaker member comprises six sheets, and the thirdand fourth sheets thereof counted from the axis of rotation of the tireconstitute said first group, while the remaining sheets thereofconstitute said second group.
 8. A pneumatic tire according to claim 1,wherein said cord elements of said breaker member are made of flexiblematerials selected from the materials consisting of natural resins,synthetic resins, glass fiber materials.
 9. A pneumatic tire having abreaker member, comprising a pair of bead portions including metalwires, a carcass extending between said pair of bead portionssubstantially in radial directions radiating from the axis of rotationof the tirE, said carcass consisting of at least one rubberized sheetincluding cord elements made of flexible material, a tread portionmounted on said carcass with a suitable spacing between them, and abreaker member inserted between said tread portion and said carcass,said breaker member consisting of at least a first group of sheetsincluding cord elements of a certain modulus of elasticity and a secondgroup of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair of sheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial direction by a second angle onopposite sides of the equator, said second angle being larger than saidfirst angle, said first angle being in the range of 5* to 17*, saidsecond angle being in the range of 13* to 50*, and said certain modulusof elasticity of the first group of sheets being smaller than that ofsaid different modulus of elasticity of said second group of sheets,said cord elements of said second group of sheets intersect with atleast one parallelogram formed by the cord elements of said first groupof sheets both at an apex of a large interior angle of said oneparallelogram and at about the middle point of that side of said oneparallelogram which is opposite to said apex thereof.
 10. A pneumatictire having a breaker member, comprising a pair of bead portionsincluding metal wires a carcass extending between said pair of beadportions substantially in radial directions radiating from the axis ofrotation of the tire, said carcass consisting of at least one rubberizedsheet including cord elements made of flexible material, a tread portionmounted on said carcass with a suitable spacing between them, and abreaker member inserted between said tread portion and said carcass,said breaker member consisting of at least a first group of sheetsincluding cord elements of a certain modulus of elasticity and a secondgroup of sheets including cord elements of a different modulus ofelasticity, said cord elements in each sheet of the breaker member beinglaid in parallel within the sheet, said first group having at least apair of sheets whose cord elements deviate from the equatorial directionof the tire by a first angle on opposite sides of said equatorialdirection, said second group having at least a pair of sheets whose cordelements deviate from said equatorial direction by a second angle onopposite sides of the equator, said second angle being larger than saidfirst angle, said first group comprising a pair of sheets including cordelements having a modulus of elasticity of 1.5 gram/denier at anelongation of 2 percent said sheets of the first group being deviatedfrom the equatorial direction of the tire by 13* on opposite sides ofsaid equatorial direction, and said second group comprising a pair ofsheets including cord elements having a modulus of elasticity of 2gram/denier at an elongation of 2 percent, said sheets of the secondgroup deviating from the equatorial direction of the tire by 33* onopposite sides of said equatorial direction.